Polystyrene is a thermoplastic with many desirable characteristics. It is clear, transparent, readily colored and easily fabricated. The family of styrene polymers includes polystyrene itself, copolymers of styrene with other vinyl monomers, polymers of derivatives of styrene and mixtures of polystyrene and styrene-containing copolymers with elastomers. Pure polystyrene is glass-like, transparent, hard, and rather brittle.
ABS (acrylonitrile, butadiene, styrene) and SAN (styrene, acrylonitrile) resins have enjoyed tremendous commercial popularity for many years as durable, temperature and solvent resistant elastomers. On the other hand, styrene plastics are commonly used for packaging, including foams and films, coatings, in appliance fabrication, for housewares and toys, lighting fixtures and in construction materials.
Common industrial methods for producing vinyl aromatic monomers, such as styrene, include a variety of purification processes, the most common one being distillation. It is well known that vinyl aromatic monomers readily polymerize when heated and that rate of polymerization increases rapidly as the temperature increases. Thermal polymerization during distillation results not only in loss of product, but it could render the finished monomer unsuitable for using without further treatment.
To prevent polymerization of vinyl aromatic monomers under distillation conditions, various inhibitor compositions have been employed. Unfortunately, although several compounds are effective against vinyl aromatic monomer polymerization under storage conditions, only some of these compounds have proved to be effective against polymerization under distillation conditions.